J/ApJ/888/89 Lya galaxies in 3 CFHTLS overdense regions (Toshikawa+, 2020)
Discovery of protoclusters at z∼3.7 and 4.9: embedded in primordial
superclusters.
Toshikawa J., Malkan M.A., Kashikawa N., Overzier R., Uchiyama H., Ota K.,
Ishikawa S., Ito K.
<Astrophys. J., 888, 89 (2020)>
=2020ApJ...888...89T 2020ApJ...888...89T
ADC_Keywords: Galaxies, spectra; Optical; Magnitudes, absolute; Ultraviolet;
Redshifts; Equivalent widths; Photometry, RI
Keywords: Lyman-break galaxies ; Galaxy environments ;
High-redshift galaxy clusters
Abstract:
We have carried out follow-up spectroscopy on three overdense regions
of g- and r-dropout galaxies in the Canada-France-Hawaii Telescope
Legacy Survey Deep Fields, finding two new protoclusters at z=4.898
and 3.721 and a possible protocluster at z=3.834. The z=3.721
protocluster overlaps with a previously identified protocluster at
z=3.675. The redshift separation between these two protoclusters is
Δz=0.05, which is slightly larger than the size of typical
protoclusters. Therefore, if they are not the progenitors of a
>1015M☉ halo, they would grow into closely located independent
halos like a supercluster. The other protocluster at z=4.898 is also
surrounded by smaller galaxy groups. These systems including
protoclusters and neighboring groups are regarded as the early phase
of superclusters. We quantify the spatial distribution of member
galaxies of the protoclusters at z=3.675 and 3.721 by fitting triaxial
ellipsoids, finding a tentative difference: one has a pancake-like
shape, while the other is filamentary. This could indicate that these
two protoclusters are in different stages of formation. We investigate
the relation between redshift and the velocity dispersion of
protoclusters, including other protoclusters from the literature, in
order to compare their dynamical states. Although there is no
significant systematic trend in the velocity dispersions of
protoclusters with redshift, the distribution is skewed to higher
velocity dispersion over the redshift range of z=2-6. This could be
interpreted as two phases of cluster formation, one dominated by the
steady accretion of galaxies and the other by the merging between
group-size halos, perhaps depending on the surrounding large-scale
environments.
Description:
We have obtained follow-up spectroscopy on three overdense regions in
the Canada-France-Hawaii Telescope Legacy Survey (CFHTLS) Deep Fields,
which are identified by T16 (Toshikawa+, 2016, J/ApJ/826/114).
We have made optical follow-up spectroscopic observations of the three
overdense regions of r- and g-dropout galaxies in the D1 and D4
fields, which are termed "D1RD01," "D1GD02," and "D4GD01" in T16.
Follow-up spectroscopy is performed for the first time for the
overdense region of D1GD02 in this study.
Our spectroscopic observations were conducted as part of Keck
Observatory programs U033D in 2015 and U130D in 2016. We used Keck II
DEIMOS with multi-object spectroscopy (MOS) mode.
83 galaxies are newly confirmed by detecting their Lyα emission
lines (Table 3).
File Summary:
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FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
targets.dat 93 5 Overview of the three overdense regions targeted
(Tables 1 and 2)
table3.dat 121 83 Observed properties of spectroscopically confirmed
dropout galaxies
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See also:
B/cfht : Log of CFHT Exposures (CADC, 1979-)
J/ApJ/621/673 : Line indices for 124 early-type galaxies (Thomas+, 2005)
J/ApJS/167/1 : Galaxy groups and clusters from SDSS (Berlind+, 2006)
J/ApJ/648/7 : z=6.5 Lya emitters in Subaru Deep Field (Kashikawa+, 2006)
J/AJ/133/2222 : Clustering of high-redshift QSOs from SDSS (Shen+, 2007)
J/A+A/461/823 : Candidate Lyα emitting galaxies (Venemans+, 2007)
J/ApJ/754/83 : UV continuum for z∼4-7 star-forming gal. (Bouwens+, 2012)
J/MNRAS/429/3272 : REFLEX II flux-limited supercluster sample (Chon+, 2013)
J/A+A/559/A2 : Redshifts toward MRC 0156-252 (Galametz+, 2013)
J/ApJ/765/87 : Chandra obs. of the 2QZ Cluster 1004+00 (Lehmer+, 2013)
J/MNRAS/436/275 : Relaxation param. of 2092 rich galaxy clusters (Wen+, 2013)
J/ApJ/769/79 : Spitzer obs. of radio-loud AGNs (CARLA) (Wylezalek+, 2013)
J/MNRAS/445/4073 : Two catalogues of superclusters (Chow-Martinez+, 2014)
J/A+A/572/A41 : VUDS Dicovery of a high-z protocluster (Lemaux+, 2014)
J/A+A/566/A1 : Flux- & volume-limited groups for SDSS gal. (Tempel+, 2014)
J/ApJ/823/11 : Candidate Lyα emitting galaxies at z∼3.8 (Dey+, 2016)
J/ApJ/826/114 : z∼3-6 protocl. in the CFHTLS deep fields (Toshikawa+, 2016)
J/ApJ/833/194 : Group of gal. in gravitational lens fields (Wilson+, 2016)
J/ApJ/845/172 : LAE cand. around bright Lyα blobs (Badescu+, 2017)
J/ApJ/834/101 : Keck/MOSFIRE spectroscopy of ZFOURGE galaxies (Tran+, 2017)
J/ApJ/859/38 : HST grism obs. of CARLA galaxy cluster cand. (Noirot+, 2018)
J/MNRAS/473/1977 : Catalogue of the HAE sample in USS 1558 (Shimakawa+, 2018)
J/ApJ/874/54 : X-ray sources in USS 1558-003 (Macuga+, 2019)
Byte-by-byte Description of file: targets.dat
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Bytes Format Units Label Explanations
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1- 6 A6 --- Reg Overdense region ID
8- 9 I2 h RAh Hour of right ascension (J2000)
11- 12 I2 min RAm Minute of right ascension (J2000)
14- 17 F4.1 s RAs Second of right ascension (J2000)
19 A1 --- DE- Sign of declination (J2000)
20- 21 I2 deg DEd Degree of declination (J2000)
23- 24 I2 arcmin DEm Arcminute of declination (J2000)
26- 29 F4.1 arcsec DEs Arcsecond of declination (J2000)
31- 39 A9 --- Pop Population
41- 43 F3.1 --- Sig [4.2/4.4] Overdensity at the peak in σ
45- 47 I3 --- Nlbg [40/153] Number of dropout galaxies whithin 3'
radius from the overdensity peak (1)
49- 51 A3 --- T16 Yes: also observed in T16
(Toshikawa+, 2016, J/ApJ/826/114)
53- 54 I2 --- Nt16 [15/60]? Number of spectroscopically observed
galaxies in T16 located within 3' radius
from the overdensity peak
56- 66 A11 "Y:M:D" Date Date of spectroscopic observation (UT)
67 A1 --- --- [,]
68- 69 I2 d Day2 ? Second day of observation if any
71- 75 A5 --- grism Keck/DEIMOS grism
77- 79 I3 min Exp [157/313] Exposure time
81- 83 F3.1 arcsec Seeing [0.7/0.9] Seeing
85- 87 I3 --- Nobs [38/101] Number of observed galaxies (2)
89- 90 I2 --- Nprev [2/20]? Number of galaxies observed
in previous observations
92- 93 I2 --- Ndet [8/29] Number of spectroscopically
detected galaxies
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Note (1): Note that DEIMOS can observe more galaxies, since its FoV is wider
than 6'.
Note (2): A DEIMOS mask can typically contain ∼90-100 slits; thus, we have
also observed dropout galaxies at other redshifts as mask fillers. For
example, the masks targeting r-dropout overdense regions include
g-dropout galaxies as well. Since such mask fillers do not belong to
the candidates of protoclusters, they are not used in this study.
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Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 6 A6 --- Reg Overdense region ID
8- 9 I2 --- ID [1/52] Identifier within reg (1)
11- 12 I2 h RAh Hour of right ascension (J2000)
14- 15 I2 min RAm Minute of right ascension (J2000)
17- 21 F5.2 s RAs Second of right ascension (J2000)
23 A1 --- DE- Sign of declination (J2000)
24- 25 I2 deg DEd Degree of declination (J2000)
27- 28 I2 arcmin DEm Arcminute of declination (J2000)
30- 33 F4.1 arcsec DEs Arcsecond of declination (J2000)
35- 39 F5.2 mag imag [24.2/27.2] CFHT i-band AB magnitude
41- 44 F4.2 mag e_imag [0.01/0.2] Uncertainty on the imag
46- 50 F5.3 --- z [3.6/5.5] Redshift (2)
52- 56 F5.3 --- e_z [0.001] Negative uncertainty on z
58- 62 F5.3 --- E_z [0.001/0.002] Positive uncertainty on z
64- 69 F6.2 mag UVMag [-22.1/-18.4] UV absolute magnitude, MUV (3)
71- 74 F4.2 mag e_UVMag [0.02/0.4] Uncertainty on the UVMag
76- 80 F5.2 --- FLya [1/84.5] Observed line flux, fLyα
82- 85 F4.2 --- e_FLya [0.2/3] FLya uncertainty
87- 91 F5.2 --- LLya [0.16/10.4] Lyα luminosity, LLyα
93- 96 F4.2 --- e_LLya [0.05/0.4] LLya uncertainty
98- 103 F6.2 0.1nm EW0 [3/183] Rest-frame Lyα equivalent width
105- 109 F5.2 0.1nm e_EW0 [0.3/76] EW0 uncertainty
111- 115 F5.2 --- Sk [-2.2/11.1] The weighted skewness, Sw
117- 121 F5.2 --- e_Sk [0.3/11.2] Sk uncertainty
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Note (1): IDs are continued from T16 (Toshikawa+, 2016, J/ApJ/826/114 ;
<[TKO2016] DNADNN NN> in Simbad); thus, ID=1-6 in the D1RD01 region and
ID=1-42 in the D4GD01 region are shown in Table 4 and Figure 9 of T16.
Note (2): The redshifts are derived by the peak wavelength of the Lyα
emission line, assuming the rest wavelength of Lyα to be 1215.6Å.
Note (3): MUV is estimated from the broadband photometry. It is derived from
r-band (i-band) magnitudes for g-dropout (r-dropout) galaxies after
correcting the contribution of the absorption of intergalactic medium
(IGM) and the Lyα emission. In this calculation, we assume flat UV
spectra (fλ∝λβ, where β=-2) and the
IGM transmission model of Madau (1995ApJ...441...18M 1995ApJ...441...18M).
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History:
From electronic version of the journal
(End) Emmanuelle Perret [CDS] 21-Jun-2021